Three-dimensional molded parts made of fiber material are used, in particular, in the automotive industry. These molded parts are used for sound insulation. They are used, for example, as door linings, rear package shelves, and vehicle ceilings. Likewise, the floor and the walls connecting the passenger compartment to the trunk space and also the passenger compartment to the engine space are lined with sound-insulating molded parts. Here, one-piece parts should be used as much as possible. The car-body plates are deformed greatly and irregularly in terms of stiffness and material savings. They feature receptacles for additional components of the vehicle and passages, for example, for cable channels and the steering-wheel column. The molded parts that are used for sound insulation must be adapted to these strongly three-dimensionally shaped chassis parts.
Three-dimensional molded parts for sound insulation, so-called acoustic parts, with unequal thickness, currently can be produced from PU foam. However, this is relatively expensive, because this type of foam is produced on the basis of crude oil. In addition, PU foam is also hard to recycle. When burned, it emits poisonous vapors.
Molded parts made of conventional fiber mats, which are produced from fiber materials by rollers, are only suitable to a limited degree. Fiber mats can only be used for weakly deformed parts. Under greater deformation, the mats rip. Also, due to the rolling method, they do not exhibit a uniform density distribution. Therefore, they frequently do not correspond to the geometrical and acoustic requirements placed on such special molded parts.
Furthermore, in the state of the art, three-dimensional nonwoven parts are known, which consist of a fiber mixture or fibers and an added bonding agent. These nonwoven parts are produced by means of a hot-molding process: a fiber mixture flows from above into a bottom mold, so that the fibers accumulate in the bottom mold. This flocking of the bottom mold is realized by means of a moving pivot channel, which can be moved above the bottom mold. After the bottom mold is filled, a top mold is placed on the bottom mold so that the dry, layered fibers are pressed. Then hot air is passed through the mold consisting of the bottom and top molds so that the fibers fuse to each other, resulting in a molded part. A disadvantage of this method is that partial flocking cannot be performed precisely, and thus, in particular, a local increase in density is not possible. Because the density of the final molded part is defined only by the accumulated fibers in a local region, the density in the molded part can be varied only in the scope of accumulation possible due to the force of gravity. Likewise, it is possible only with difficulty to reduce the weight of the entire molded part, such that certain acoustically non-critical areas feature a smaller density. However, the reduction of the total weight is very important in vehicle construction. Because the flocking of the bottom mold occurs solely according to the laws of gravity, in that, namely, the fibers are simply scattered in the mold, a high cycle time for the production of such a molded part is produced. Due to the expensive machine use times, the costs of the molded part are rather high.
Unexamined German Patent Application No. 23 18 501.5 discloses a device for producing fiber preforms. Chopped fibers are deposited against the inner surface of a horizontally rotating sieve-like mold. The feed is realized by means of a tube, which can move horizontally. The fibers laid in the mold are pressed against the mold by an external vacuum, which surrounds the outer surface of the mold. Then the fibers are coated with a plastic resin bonding agent spray, which hardens under heat. Hot air can pass through the mold filled with fibers so that the formed body hardens.
DE 35 41 073 A1 describes a method and a device for producing a starting material for molding a fiber-reinforced part. Raw fibers, which are saturated with resin, are cut into segments of predetermined length and collected in a container. The container can move so that fibers are deposited according to the molded part to be produced. However, this method has the disadvantages described above.
EP 1 250 991 A1 discloses a production system for automatic production of preforms. The system comprises two cells each with a molded part, a fan for both cells, and an automatic feed unit in order to supply endless fibers to the molds. The supply unit features several sleeves in order to reduce friction and to improve the guidance of the fibers.
The problem to be solved by the present invention is to produce three-dimensional molded parts that feature areas of different thickness and in which the density can be varied locally in a simple and efficient way. In this way, the density variations within the molded part should be exactly reproducible so that even for large quantities identical parts can be produced.